1. Field of the Invention
This invention relates to a method for manufacturing a cylindrical armature used in a low-inertia DC motor or the like.
2. Description of the Prior Art
In a conventional cylindrical armature of this type, an armature winding is arranged cylindrically and glass tapes for the dual purpose of insulation and reinforcement for transmission of torque generated in the armature winding to the armature shaft are wound on the outer and inner peripheral surface of the cylindrical armature winding and then hardened with resin.
The insulating layer formed by the glass tape, however, is unable to protect the armature sufficiently from the torsional forces generated when the armature is rotating.
An alternative conventional method is also proposed in which a glass filament impregnated with resin is uniformly wound spirally to form an insulating layer. In forming such an insulating layer of glass filament, the glass filament is uniformly wound on the inner and outer peripheral surfaces of the cylindrical armature winding in continuous reciprocation in the direction of the axis of the winding, resulting in an undesirable unevenness of the glass filament occurring at the longitudinal turning points.
The presence of such an uneveness of the insulating material on the outer peripheral surface of the cylindrical winding increases the thickness of the side wall of the cylindrical armature. This unnecessarily enlarges the gap between the armature and the stator, thus deteriorating the motor performance.
According to another conventional method for overcoming the above-mentioned shortcoming, the glass filament is wound also on the part of the armature winding other than the effective part thereof to attain a uniform thickness of the insulating layer, in such a manner that the turning points of winding of the glass filament are situated at that extraneous part, thus achieving a uniform thickness of the effective part of the insulating layer.
In the last-mentioned method, however, the insulating layer of the glass filament is inevitably and undesirably wound on the outer peripheral surface of a commutator firmly fitted on the shaft as well as on the shaft itself. This requires a special post-treatment for removal of the undesirable portion of the insulating layer which is disadvantageous for working labor efficiency.